Nuclear reactors and coolant therefor

ABSTRACT

Carbon dioxide for the cooling of a carbon dioxide-cooled, graphite-moderated nuclear reactor is mixed with hydrogen and passed over a catalyst which promotes the reaction between carbon dioxide and hydrogen to produce methane. The hydrogen is obtained by electrolysis of water in plant which may also produce argonfree oxygen for consumption in a carbon monoxide/oxygen recombination unit, converting carbon monoxide formed in the coolant to carbon dioxide.

United States Patent [72] Inventors Geoffrey Baguley Croft, Warrington,England; Daniel A. Shields, San Carlos, Calif. [21] Appl. No. 745,608

[22] Filed July 17, 1968 [45] Patented Nov. 9, 1971 [73] Assignee UnitedKingdom Atomic Energy Authority London, England [54] NUCLEAR REACTORSAND COOILANT THEREFOR 4 Claims, 1 Drawing Fig.

52 vs. C] 176/38, 176/92, 260/4496 [51] 1nt.C1 G2lc 15/28 [50] Field 01Search 176/38, 92', 260/449.6

[56] References Cited UNITED STATES PATENTS 3,108,051 10/1963 Lindstrom3,427,221 2/1969 Campion 176/92 X FOREIGN PATENTS 1,381,937 11/1964France 176/38 1,102,764 2/1968 Great Britain 176/38 PrimaryExaminer-Leland A. Sebastian Assistant ExaminerHarvey E. BehreindAItorneyLarson, Taylor and Hinds ABSTRACT: Carbon dioxide for thecooling ofa carbon dioxide-cooled, graphite-moderated nuclear reactor ismixed with hydrogen and passed over a catalyst which promotes thereaction between carbon dioxide and hydrogen to produce methane. Thehydrogen is obtained by electrolysis of water in plant which may alsoproduce argon-free oxygen for consumption in a carbon monoxide/oxygenrecombination unit, converting carbon monoxide formed in the coolant tocarbon dioxide.

BACKGROUND OF THE INVENTION This invention relates to nuclear reactorsand to the coolant therefor.

In carbon dioxide-cooled, graphite-moderated nuclear reactors reactionoccurs between the graphite and the carbon dioxide under irradiation,resulting in corrosion of the graphite, and it is considered desirablein highly-rated reactors to add small amounts of methane to the coolantin order to inhibit the graphite-carbon dioxide reaction. Methane isdestroyed in the reactor however and may not always be available in thequantity and purity required for makeup; even if it is available it isexpensive. Accordingly it has been suggested that methane should beproduced from the radiolytic decomposition products of the carbondioxide coolant and methane (that is to say, carbon monoxide, hydrogenand water) the reaction being promoted by passing the coolant over asuitable catalyst. It has further been suggested that the yield ofmethane may be increased by the addition of water to the circulatingcoolant before passing it over the catalyst.

SUMMARY OF THE INVENTION According to the present invention carbondioxide for the cooling of a carbon dioxide-cooled, graphite-moderatednuclear reactor is mixed with hydrogen and passed over a catalystadapted to promote the reaction between carbon dioxide and hydrogen toproduce methane, the hydrogen being obtained by electrolysis.

The electrolytic plant in which the hydrogen is produced may alsoproduce argon-free oxygen for consumption in a carbon monoxide/oxygenrecombination unit. Such a unit removes carbon monoxide from the coolantcirculating through the reactor by converting the carbon monoxide tocarbon dioxide. This carbon dioxide may be used as the feed to whichhydrogen is added but it should be substantially freed of carbonmonoxide by passing over copper oxide, for example, as carbon monoxideinterferes with the reaction between hydrogen and carbon dioxide. In analternative the hydrogen is added to a bleed from the carbon dioxidemakeup feed line to the reactor coolant circuit. One suitable catalystfor promoting the reaction between carbon dioxide and hydrogen toproduce methane is nickel. Catalyst temperatures of 300-400C. aregenerally required. Water is produced in the reaction and the majorityof this water is preferably removed before the feed is introduced intothe main reactor coolant circuit. This may be done in a conventionalwater cooler and separator.

The proportions of hydrogen and carbon dioxide in the feed to thecatalyst feed are selected to give the desired concentration of methanein the reactor coolant.

DESCRIPTION OF THE DRAWING The invention will now be described withreference to the accompanying drawing which is a diagrammaticarrangement of an auxiliary coolant circuit for a nuclear reactor.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing is shown anuclear reactor 1. Carbon dioxide coolant leaves the reactor by duct 2at the rate of 100,000 lbs./hr. Ten percent of this gas (10,000 lbs/hr.)is bled off by duct 3 for dryer regeneration as explained below. Theremainder (90,000 lbs/hr.) is led by duct 4 through heat exchanger 5 andwater cooler 6 then by duct 15 to dryer 7 be fore returning to thereactor via duct 81, heat exchanger 5 and duct 9, A further bleed line10 takes 15,000 lbs/hr. of coolant through a carbon monoxide/oxygenrecombination unit 11 after mixing with 44 lbs/hr. oxygen, the gas thenbeing returned to cut 4. The oxygen is supplied from an electrolyticplant 12. The plant 12 also provides 5.5-6.0 lbs/hr. hydrogen to acatalyst bed 13 having a feed of 30 lbs/hr. carbon dioxide.

The catalyst bed contains a nickel catalyst maintained at 300-400 C. andthe hydrogen and carbon dioxide react to produce methane in accordancewith the equation:

CO -+-4H CH,+ 2H O Water is also produced and most of this is removed ina water cooler and separator 14 before the feed gas joins duct 15 topass through the dryer 7 and heat exchanger 5 to the reactor 1. A seconddryer 7 is also provided. One dryer is regenerated while the other is inuse. Regeneration is effected by passing the bleed of hot gas from duct3 (10,000 lbs/hr.) through the dryer in the reverse direction to flowfor drying, the wet gas then being passed through the water cooler andseparator I4 with the feed gas of carbon dioxide and methane.

We claim:

1. In a method of inhibiting the reaction between a carbon dioxidecoolant and a graphite moderator in a nuclear reactor, which methodincludes the introduction of methane into the coolant, the improvementcomprising the steps of preparing hydrogen by electrolysis of water,mixing the hydrogen with carbon dioxide, passing the mixture over acatalyst adapted to promote the reaction between carbon dioxide andhydrogen to produce methane in the mixture, removing water from themethane-containing mixture, and feeding the resulting mixture to thenuclear reactor coolant circuit.

2. A method as claimed in claim 1 comprising the additional steps ofalso preparing oxygen by electrolysis of the water and feeding theoxygen and carbon dioxide coolant which has circulated through thereactor to a plant to convert to carbon dioxide carbon monoxide presentin the coolant from the reactor.

3. A method as claimed in claim 2 wherein the carbon dioxide with whichthe hydrogen is mixed is taken from the output of the conversion plant.

4. A method as claimed in claim 1 wherein the hydrogen is added to thecarbon dioxide feed to the reactor coolant.

2. A method as claimed in claim 1 comprising the additional steps ofalso preparing oxygen by electrolysis of the water and feeding theoxygen and carbon dioxide coolant which has circulated through thereactor to a plant to convert to carbon dioxide carbon monoxide presentin the coolant from the reactor.
 3. A method as claimed in claim 2wherein the carbon dioxide with which the hydrogen is mixed is takenfrom the output of the conversion plant.
 4. A method as claimed in claim1 wherein the hydrogen is added to the carbon dioxide feed to thereactor coolant.